GHSA-p6mc-m468-83gw CVE-2020-8203

Prototype Pollution in lodash

High RubyGemsnpm

Severity: 7.4 / 10; High · CVSS 3.1
Exploit chance (EPSS): 5.21%; Chance of exploitation in the next 30 days. Higher than 92.50% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-770 Allocation of Resources Without Limits or Throttling; CWE-1321 Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Fix: Available; 3 packages have a fixed version

Description

Versions of lodash prior to 4.17.19 are vulnerable to Prototype Pollution. The functions pick, set, setWith, update, updateWith, and zipObjectDeep allow a malicious user to modify the prototype of Object if the property identifiers are user-supplied. Being affected by this issue requires manipulating objects based on user-provided property values or arrays.

This vulnerability causes the addition or modification of an existing property that will exist on all objects and may lead to Denial of Service or Code Execution under specific circumstances.

Affected versions

RubyGems

Package	Vulnerable	Fixed in
lodash-rails	`>= 3.7.0, < 4.17.19`	`4.17.19`
lodash-rails	`>= 3.7.0, < 4.17.19`	`4.17.19`

npm

Package	Vulnerable	Fixed in
lodash	`>= 3.7.0, < 4.17.19`	`4.17.19`
lodash	`>= 3.7.0, < 4.17.19`	`4.17.19`
lodash-es	`>= 3.7.0, < 4.17.20`	`4.17.20`
lodash-es	`>= 3.7.0, < 4.17.20`	`4.17.20`
lodash.pick	`>= 4.0.0, <= 4.4.0`	No fix yet
lodash.pick	`>= 4.0.0, <= 4.4.0`	No fix yet
lodash.set	`>= 3.7.0, <= 4.3.2`	No fix yet
lodash.set	`>= 3.7.0, <= 4.3.2`	No fix yet
lodash.setwith	`<= 4.3.2`	No fix yet
lodash.setwith	`<= 4.3.2`	No fix yet
lodash.update	`<= 4.10.2`	No fix yet
lodash.update	`<= 4.10.2`	No fix yet
lodash.updatewith	`<= 4.10.2`	No fix yet
lodash.updatewith	`<= 4.10.2`	No fix yet

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

lodash-rails RubyGems → `4.17.19`

bundler

bundle update lodash-rails # Gemfile: gem "lodash-rails", ">= 4.17.19"

lodash npm → `4.17.19`

npm

npm install lodash@4.17.19

yarn

yarn add lodash@4.17.19

pnpm

pnpm add lodash@4.17.19

lodash-es npm → `4.17.20`

npm

npm install lodash-es@4.17.20

yarn

yarn add lodash-es@4.17.20

pnpm

pnpm add lodash-es@4.17.20

Severity breakdown

CVSS 3.1 7.4

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H

Attack vector: Network
Attack complexity: High
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: High

Weakness

CWE-770: Allocation of Resources Without Limits or Throttling

The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

How to prevent it

Requirements: Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
Architecture and Design: Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place, and it will help the administrator to identify who is committing the abuse. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, typically by using increasing time delays uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution can be difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply requires more resources on the part of the attacker.
Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
Architecture and Design, Implementation: If the program must fail, ensure that it fails gracefully (fails closed). There may be a temptation to simply let the program fail poorly in cases such as low memory conditions, but an attacker may be able to assert control before the software has fully exited. Alternately, an uncontrolled failure could cause cascading problems with other downstream components; for example, the program could send a signal to a downstream process so the process immediately knows that a problem has occurred and has a better chance of recovery. Ensure that all failures in resource allocation place the system into a safe posture.
Operation, Architecture and Design: Use quotas or other resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users. Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).

CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.

How to prevent it

Implementation: By freezing the object prototype first (for example, Object.freeze(Object.prototype)), modification of the prototype becomes impossible.
Architecture and Design: By blocking modifications of attributes that resolve to object prototype, such as proto or prototype, this weakness can be mitigated.
Implementation: When handling untrusted objects, validating using a schema can be used.
Implementation: By using an object without prototypes (via Object.create(null) ), adding object prototype attributes by accessing the prototype via the special attributes becomes impossible, mitigating this weakness.
Implementation: Map can be used instead of objects in most cases. If Map methods are used instead of object attributes, it is not possible to access the object prototype or modify it.

References

Advisories

Fixes and patches

Packages

github.com/lodash/lodash

Timeline

Jul 15, 2020 Published
Aug 12, 2025 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-r5fr-rjxr-66jc lodash vulnerable to Code Injection via `_.template` imports key names	Critical	Also affects lodash
GHSA-f23m-r3pf-42rh lodash vulnerable to Prototype Pollution via array path bypass in `_.unset` and `_.omit`	Medium	Also affects lodash
GHSA-xxjr-mmjv-4gpg Lodash has Prototype Pollution Vulnerability in `_.unset` and `_.omit` functions	Medium	Also affects lodash
GHSA-29mw-wpgm-hmr9 Regular Expression Denial of Service (ReDoS) in lodash	Medium	Also affects lodash
GHSA-35jh-r3h4-6jhm Command Injection in lodash	High	Also affects lodash
GHSA-x5rq-j2xg-h7qm Regular Expression Denial of Service (ReDoS) in lodash	Medium	Also affects lodash
GHSA-jf85-cpcp-j695 Prototype Pollution in lodash	Critical	Also affects lodash
GHSA-4xc9-xhrj-v574 Prototype Pollution in lodash	High	Also affects lodash

Credits: G-Rath, bengry, greengeko, jkmartindale, mitchell-codecov, tompazourek

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